Common smoke detectors are designed to provide a warning by generating a visual and/or audible alarm. Smoke detectors are powered by alternating current (AC), batteries or a combination of both. AC-powered smoke detectors with battery backup are typically considered to be the primary detectors, while smoke detectors powered by batteries alone are considered to be supplemental detectors.
Both smoke detectors powered only with a battery, as well as AC-powered smoke detectors with battery backup usually generate a low battery trouble signal once the battery power diminishes below a prescribed level. The low battery trouble signal is typically a single short horn beep emitted at regular intervals, such as every minute. A benefit of the low battery trouble signal is that it alerts the home dweller or user that the battery power is low and that the battery needs to be replaced. In most cases, there is a time period ranging from days to a week of battery power remaining before the detector is inoperable on battery power alone. Thus, there is ample time for the user to replace the battery after being alerted by the low battery trouble signal.
One drawback with conventional AC-powered with battery backup type smoke detectors is that once the low battery trouble signal is initiated, the trouble signal continues until the battery is replaced. This situation can occur if there is no new battery on hand. In a battery-powered detector, removing the battery will stop the signal, but renders the detector useless in a fire situation. In an AC-powered detector with battery backup, the detector will typically continue to emit the trouble signal once the battery is removed. Thus, in the AC-powered with battery backup case, the only recourse to stop the trouble signal is to shut off the AC power to the detector or disconnect the detector.